The overall objective of this proposal is to identify and characterize putative stem/progenitor cells in the adult pancreas. The identification of such cells would facilitate the development of a cell replacement therapy for patients with diabetes. Such therapy, though highly effective, is currently limited by the shortage of transplantable islets from cadaver tissue. Adult progenitors would be a particularly attractive source for the differentiation of replacement insulin-producing beta-cells, as they could possibly be isolated from the patient's own pancreas, thereby avoiding the immune response associated with the transplantation of foreign tissue. It is, however, still unclear whether a stem or progenitor cell population resides in the pancreas beyond the embryonic period. In preliminary studies, we have identified the transcription factor SOX9 as a marker for progenitor cells in the embryonic pancreas and found that Sox9 is essential for their expansion and maintenance. Strikingly, its expression persists in the adult pancreas exclusively in a subset of ductal cells;a cell type that is regarded as a potential reservoir of pancreatic stem/progenitor cells. Given the crucial role of SOX9 in maintaining undifferentiated, pluripotent progenitors of the embryonic pancreas, we hypothesize that this factor also marks and maintains a stem cell compartment in the adult pancreas. Experiments are proposed to test whether SOX9 plays a role in pancreas regeneration and whether the cells marked by SOX9 in adult pancreas can function as pluripotent pancreas progenitor cells. Using inducible gene ablation, Aim 1 is to define the role of Sox9 in pancreatic cell differentiation and maintenance throughout development and adulthood. Aim 2 examines if Sox9 is required for pancreas regeneration after partial pancreatectomy or STZ treatment. Aim 3 will define whether Sox9-expressing cells have characteristics and properties of multipotential stem/progenitor cells. This will be tested by transcriptional profiling of isolated cells and by tracking their fate in cell transplantation experiments.